NaN Velocity Error in ALE Domain

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Furkan Keleş

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Dec 7, 2021, 9:10:07 AM12/7/21
to LS-DYNA2
Dear all,

I am working on a 2D axisymmetrical explosion simulation using ALE elements and I keep getting NaN velocity errors. Nodes with NaN velocities are always near the boundaries of different multi-material groups such as water and explosive. You can see this in the picture below.
I am sharing material parameters and most of the keywords I use in the .k file attached. 

Any advice on how to go about solving this problem would be most appreciated.

Thank you,
Furkan.Sample.png
Sample.k

l...@schwer.net

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Dec 7, 2021, 10:40:13 AM12/7/21
to Furkan Keleş, LS-DYNA2

By chance are you using triangular elements?

Such elements, where the third and fourth node numbers are identical, do not work well with MM-ALE.                 --len

Furkan.

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image001.png

Furkan Keleş

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Dec 7, 2021, 12:19:46 PM12/7/21
to L...@schwer.net, LS-DYNA2
Yes, I do have triangular elements in some parts of the mesh. I will look into that, thanks. 

Are there any other possible reasons for this problem to occur?

Furkan.


On 7 Dec 2021, at 18:40, <l...@schwer.net> <l...@schwer.net> wrote:

By chance are you using triangular elements?

Such elements, where the third and fourth node numbers are identical, do not work well with MM-ALE.                 --len

 

From: ls-d...@googlegroups.com <ls-d...@googlegroups.com> On Behalf Of Furkan Keles
Sent: Tuesday, December 7, 2021 6:10 AM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] NaN Velocity Error in ALE Domain

 

Dear all,

 

I am working on a 2D axisymmetrical explosion simulation using ALE elements and I keep getting NaN velocity errors. Nodes with NaN velocities are always near the boundaries of different multi-material groups such as water and explosive. You can see this in the picture below.

I am sharing material parameters and most of the keywords I use in the .k file attached. 

 

Any advice on how to go about solving this problem would be most appreciated.

 

Thank you,

Furkan.<image001.png>

James M. Kennedy

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Dec 7, 2021, 12:31:43 PM12/7/21
to Furkan Keleş, LS-DYNA2

Dear Furkan,

 

I got these errors when I attempted to run your data.

 

*** Error 10380 (KEY+380)

     *ALE_MULTI-MATERIAL_GROUP

     Element formulation/Element type mis-matched

     Part ID 5, Secion ID 1

     ELFORM 14, Element type shell

 *** Error 10380 (KEY+380)

     *ALE_MULTI-MATERIAL_GROUP

     Element formulation/Element type mis-matched

     Part ID 2, Secion ID 1

     ELFORM 14, Element type shell

 *** Error 10380 (KEY+380)

     *ALE_MULTI-MATERIAL_GROUP

     Element formulation/Element type mis-matched

     Part ID 17, Secion ID 1

     ELFORM 14, Element type shell

 *** Error 10380 (KEY+380)

     *ALE_MULTI-MATERIAL_GROUP

     Element formulation/Element type mis-matched

     Part ID 4, Secion ID 1

     ELFORM 14, Element type shell

 *** Error 10380 (KEY+380)

     *ALE_MULTI-MATERIAL_GROUP

     Element formulation/Element type mis-matched

     Part ID 14, Secion ID 1

     ELFORM 14, Element type shell

 *** Error 10133 (KEY+133)

     input data failed with: 10 errors

 

Sincerely,

James M. Kennedy

KBS2 Inc.

December 7, 2021

 

From: ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com] On Behalf Of Furkan Keles
Sent: Tuesday, December 07, 2021 8:10 AM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] NaN Velocity Error in ALE Domain

 

Dear all,

--

image001.png

Furkan Keleş

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Dec 7, 2021, 12:49:15 PM12/7/21
to James M. Kennedy, LS-DYNA2
Dear James,

Thank you for your response. I am sorry for not pointing it out earlier, .k file I shared is not the actual file I use. I shared it because it has the same control keyword values I use and I suspected those might be the reason for the error.

My simulation initiates and runs without a problem for a while before terminating due to NaN velocity errors pointing to nodes in the ALE domain.

Furkan.<image001.png>

James M. Kennedy

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Dec 7, 2021, 1:41:50 PM12/7/21
to Furkan Keleş, L...@schwer.net, LS-DYNA2

Dear Furkan,

 

Some notes I found from a number of years ago.

 

--------------------------------------

 

Another modeling issue (after modifying void mesh) I would expect

would cause issues (at least as I read). I observed velocity issues at

the triangular meshed element.

 

--------------------------------------

 

Using the guideline below, I would say that triangular elements would

not be recommended.

Hexahedral elements with reasonable aspect ratios should be used for the
initial ALE mesh. Degenerate element shapes, such as tetrahedrons and
pentahedrons, should be avoided as they lead to reduced accuracy and
perhaps numerical instability during the advection

LS-DYNA Aerospace Working Group, "Modeling Guidelines Document",

Version 12-1, June, 2012 (Section 4.0 ALE Modeling Guidelines).

http://awg.lstc.com/tiki/tiki-download_file.php?fileId=167

 

--------------------------------------

 

Another comment I found:

 

Do you have the proper meshing that allows the material to advect or to be

transported away from its original configuration? One should work with a

real nice orthogonal fluid domain to allow the advection to act easily?

 

--------------------------------------

 

Sincerely,

James M. Kennedy

KBS2 Inc.

December 7, 2021

 

 

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